(a) Field of the Invention
This invention relates to shutters for photographic cameras and, more particularly, to a program type shutter whereby a flash-photographing is made possible at all shutter speeds.
(B) Description of the Prior Art
Generally, in a so-called program shutter wherein shutter blades are also diaphragm blades, the operated amount of the blades varies in each photographing in response to the brightness of an object to be photographed through an EE mechanism and the diaphragm aperture and shutter speed are simultaneously automatically set.
A conventional program shutter shall be briefly explained in the following. It is so arranged that, when a release button is first pushed, by its initial operation, a stopper position will be determined by the connection with an exposure meter having a CdS cell as a light receiving element, when the button is further pushed in, shutter blades will open at a constant speed, in case an object to be photographed is bright, by a present stopper, the shutter blades will close when they open slightly, for a dark object to be photographed, the stopper position will vary and the blades will fully open and then close and, even in an exposure intermediate between them, the combination of the diaphragm aperture and shutter speed will be determined continuously and steplessly.
In the case of making a flash-photographing by using such conventional program shutter as is described above, as described above, the operated amount of the shutter blades will vary each time in response to the brightness of the object to be photographed and therefore it will be difficult to directly operate a synchrocontact by the opening and closing operation of the shutter blades at all shutter speeds. In the case of making a flash photographing, unless the time of fully opening the shutter blades and the time when the flash light reaches the maximum brightness are made to coincide with each other, no efficient flash-photographing will be made. However, in the program shutter wherein the shutter blades are also diaphragm blades as described above, the time of starting the shutter blades is always fixed, the time of fully opening the shutter blades is different depending on the shutter speed to be controlled and therefore it is difficult to synchronize the time when the flash light reaches the maximum brightness with the time of fully opening the shutter blades at all shutter speeds.
Therefore, if the shutter speed is constant and only the diaphragm aperture is made variable, the above described defects will be anyhow eliminated. Therefore, it is generally practiced to adopt a so-called flashmatic system whereby, if the guide number of a flash bulb or strobobulb to be used is selected and the distance adjusting ring of the camera is operated, the shutter speed will be set and the diaphragm will vary as operatively connected with the movement of the distance adjusting ring. In such case, needless to say, the EE mechanism will not operate.
However, in the case of selecting the shutter speed to be of a specific value as described above, in consideration of the case of a general photographing, the shutter speed will not be able to be selected to be in a too high speed range and will be therefore usually set near 1/30 second. As a result, there are defects that the camera-shake will be likely to affect that, when an object moving at a high speed is photographed, the image will be likely to flow and that, when a figure at a window is photographed with a reverse light, the exposure will be excessive and a so-called daytime-synchrophotographing in which a flash light is utilized as an auxiliary light will not be made.
In order to make a daytime-synchrophotographing, it is necessary to make the EE mechanism work even at the time of a flash-photographing.
There have been conceived various methods of effectively working the EE mechanism not only at the time of a daytime-synchrophotographing but also at the time of a flash-photographing in the conventional program shutter. For example, there is a method wherein, as described above, the stopper for determining the operated amount of shutter blades is used as a synchrocontact. According to this method, when the shutter blades contact the stopper, they will begin to close and therefore the moment when they contact the stopper will be the time of fully opening the shutter blades. Therefore, if the synchrocontact is so made as to close when the blades contact the stopper, an efficient flash-photographing will be made.
However, in case such movable synchrocontact system as is described above is utilized, there will be such defects as are mentioned below. That is to say, as the synchrocontact moves, the arrangement will be complicated. As the contact time of the contact is instantaneous, the efficiency will be low. Further, due to the stagger or the like of the shutter blades, a discrepancy will be produced between the actual diaphragm aperture and the time when the flash is lighted by the synchroswitch and no favourable photographing will be made. Further, it can be used only as of an X-synchrocontact but can not be used as of an M-synchrocontact.